This invention relates to a process and apparatus for the vaporization of relatively small amounts of liquefied, low-boiling gases.
A number of low-boiling gases, for example oxygen, nitrogen, argon, or natural gas are frequently handled in the liquid phase in order to obviate or at least mitigate the problems connected with transportation or storage of these gases in the gaseous phase. The great reduction in volume resulting from liquefaction has led, for example, in the absence of pipeline systems, to the extensive practice of transporting natural gas in the liquid form from its source to consumption sites. Natural gas is also liquefied for storage purposes, i.e. gas is withdrawn from a natural gas network during times of low demand and stored to cover peak demands, the gas being liquefied in so-called peak-shaving plants and, when required, revaporized and fed back into the natural gas network. Finally, oxygen, nitrogen, argon, or other gases required in a plurality of applications are frequently obtained in the liquid phase and transported to their consumption sites in the liquid phase and are there revaporized.
In all such cases, considerable energy is required both for liquefying the gases and for their subsequent revaporization. Nevertheless, since the economic advantages attainable by the use of liquid phase transportation or storage more than offset this energy expenditure, the aforesaid liquefaction processes are widely employed.
During the revaporization of the liquefied gases at the consumption site, a large percentage of the energy expended during liquefaction can theoretically be recovered. Therefore, several proposed processes have been made to recover the refrigeration value of liquid natural gas, the latter being commonly transported to consumer sites, unloaded in liquefied natural gas terminals, and after vaporization, introduced into a distribution network. ("Refrigeration value" is interchangeably called refrigeration or cold content, or just cold.) Such processes relate, for example, to coupling with an ethylene plant (French Pat. No. 1,458,194), with air fractionation plants, or with refrigeration plants (Hydrocarbon Processing, November 1974, page 97). In all heretofore proposed processes, liquefied natural gas is vaporized continuously and in very large quantities so that the refrigeration values produced during vaporization can also be transferred continuously and with great reliability to a refrigeration consumer, which, in turn, is a prerequisite for the successful operation of such plants.
In contrast thereto, if only a comparatively minor amount, e.g., less than about 1000 Nm.sup.3 per hour, of a liquefied gas were vaporized, or vaporization did not take place continuously, the refrigeration values were not utilized heretofore because the installation of a plant suitable for using such cold would not be economic; rather, vaporization merely took place in heat exchangers heated by air, water, or other heat-transfer agents without use of the cold content.